(1) Field of Invention
The present invention relates to wall constructions, and more particularly refers to studs which may be utilized to form fire-retardant or fire-rated wall structures particularly for use in enclosing open shafts in multi-story buildings such as offices and high-rise apartments, and to the wall structures formed therewith.
(2) Description of the Prior Art
Walls enclosing shafts such as air return shafts, elevator shafts, and stairwell shafts commonly separate the shafts from other rooms such as corridors, toilets, and utility rooms. With increasing governmental concern for promoting safety for occupants of public buildings, manufacturers of building products have sought to provide shaft walls meeting at least minimal safety requirements, while at the same time, providing builders with materials that are both easy to install and low in cost.
Two of the most important of these safety requirements concern wind loading and fire ratings. Destructive wind loading is of particular concern where the shaft is an air return shaft or an elevator shaft, where pressures or vacuums are developed which load the shaft wall up to 15 pounds per square foot in excess of atmospheric pressure.
Cavity walls, and particularly those utilized for enclosing elevator shafts, stairwells, and air return shafts, are continually being subjected to increasingly stringent fire code requirements. The trend is to require such walls to meet or surpass certain fire ratings measured pursuant to ASTM E-119 Fire Rating Test. Elevator shaft walls require, for example at least a 2-hour rating. Where the wall system is "unbalanced", increasingly, code enforcement organizations are requiring that the rating be achieved from both sides of the wall. To pass such tests, each transfer through the metal studs used to construct such walls must be substantially reduced. At the same time, however, the stud must still retain a sufficient degree of structural strength, and in addition, must meet economic requirements. Moreover, the engagement of the stud with the wall panels which they support must be of such nature that construction is achieved with a minimum of required labor and materials. The structure must, nevertheless, withstand the requirements of accurate and complete engagement of the panels and studs, to ensure that the fire rating will be achieved.
The above fire problems concerning shafts can also be said to apply to long corridors in buildings, which in effect are horizontal, rather than vertical, shafts. Thus, without adequate fire ratings, a corridor wall easily transmits the fire throughout the floor as the fire proceeds along the corridor.
To solve these and other problems, early building shaft walls were commonly built up and lined with various types of block masonry, including both concrete and gypsum block. While block masonry has proved suitable for many applications, it has been found to be undesirable in those situations where the shaft rises to great heights. Further, block masonry structures cannot withstand high wind loading. Because of their great weight, concrete block masonry materials require supporting structures of great weight and strength. An additional problem is that these heavy materials give rise to problems in their installation. Those skilled in installing the above-described shaft lining materials are forced to handle them at dangerously high levels.
Walls of the type described and related structures have been disclosed in the prior art, and particularly in U.S. Pat. Nos. 3,740,912, 3,702,044, 3,609,933, 3,016,116, 3,094,197, 999,752, 3,495,417, 3,271,920, 3,839,839, and many others. However, even though many of the structures disclosed in these patents have proven to be highly satisfactory, the search has continued to provide wall structures of the type described of greater strength, and greater fire-retardant properties.